Form com área transparente no Lazarus/Windows

Recentemente precisei criar um form com área interna transparente no Lazarus. Pesquisando no Google, encontrei uma dica para Delphi que foi facilmente adaptado para meu caso.

	unit Unit1;
	{$mode objfpc}{$H+}
	interface
	uses
	Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, Spin, Windows;
	type
	{ TForm1 }
	TForm1 = class(TForm)
	Button1: TButton;
	SpinEdit1: TSpinEdit;
	SpinEdit2: TSpinEdit;
	SpinEdit3: TSpinEdit;
	SpinEdit4: TSpinEdit;
	procedure Button1Click(Sender: TObject);
	procedure FormCreate(Sender: TObject);
	procedure FormResize(Sender: TObject);
	private
	{ private declarations }
	public
	{ public declarations }
	procedure NewWindowRgn;
	end;
	var
	Form1: TForm1;
	implementation
	{$R *.lfm}
	{ TForm1 }
	// Area tranparente
	// Adaptado a partir de "Get transparent form - Forms - Tips & Tricks - Greatis Delphi Pages"
	// http://www.greatis.com/delphicb/tips/lib/forms-transpform.html
	procedure TForm1.NewWindowRgn;
	var
	FormRgn, NewRgn: THandle;
	begin
	FormRgn := CreateRectRgn(0, 0, Screen.Width, Screen.Height);
	NewRgn:= CreateRectRgn(
	SpinEdit1.Value,
	SpinEdit2.Value,
	SpinEdit3.Value,
	SpinEdit4.Value);
	CombineRgn(FormRgn, FormRgn, NewRgn, RGN_DIFF);
	SetWindowRgn(Handle, FormRgn, True);
	end;
	procedure TForm1.FormCreate(Sender: TObject);
	begin
	HorzScrollBar.Visible:=False;
	VertScrollBar.Visible:=False;
	NewWindowRgn;
	end;
	procedure TForm1.Button1Click(Sender: TObject);
	begin
	NewWindowRgn;
	end;
	procedure TForm1.FormResize(Sender: TObject);
	begin
	NewWindowRgn;
	end;
	end.

view raw gistfile1.pas hosted with ❤ by GitHub

Infelizmente esta dica funciona apenas no Windows (não esquecer de incluir a unidade Windows na cláusula Uses).

Adaptado a partir de Get transparent form - Forms - Tips & Tricks - Greatis Delphi Pages.

[]'s,

Ericson Benjamim.